OF THE INVENTION
The fundamental configuration of a TE.sub.10 rectangular to TE.sub.01 circular waveguide mode launcher as developed by P. Marie in 1956 (described in U.S. Pat. No. 2,859,412) is shown in perspective in FIG. 1 as containing three series-coupled stages A, B and C. The first or input stage A, into which a TE.sub.10 rectangular mode wave is applied via a rectangular-shaped input end 11, is formed as a "folded E-plane tee" for converting a TE.sub.10 rectangular mode wave to a TE.sub.20 rectangular mode wave to be emitted at a rectangular shaped output end thereof that feeds section B. Preferably, the first conversion stage A is configured as an improved dual wedge stage as shown in FIG. 2 and described in U.S. Pat. No. 4,620,163 issued Oct. 28, 1986, entitled "TE.sub.10 Rectangular to TE.sub.01 Circular Waveguide Mode Launcher", assigned to the Assignee of the present application and the disclosure of which is incorporated by reference herein.
As shown in FIG. 2 and described in the above-referenced patent, the first conversion stage A has a first open-ended wedge-shaped waveguide section 11 which tapers to a vertex 12 at an open output end 13, and a second open-ended wedge-shaped waveguide section 15 which tapers to a vertex 16 at an input end 14. The first wedge-shaped waveguide section 11 is integrally coupled with the second wedge-shaped waveguide section 15 so that the vertex 12 of the first section 11 forms part of an edge of the output end 13 of the second section and the vertex 16 of the second section forms part of an edge of the input end 14 of the first section. Advantageously, with this improved configuration, not only is performance improved but also the input stage is easier to manufacture.
The second or middle stage B of the overall mode launcher configuration employs a TE.sub.20 rectangular to crossed TE.sub.20 rectangular mode converter, shown in perspective in FIG. 3, for gradually changing the TE.sub.20 rectangular mode output wave from stage A at input end 21 to an `X` configuration at output end 22. For this purpose, input end of middle stage B has a rectangular-shaped opening defined by a pair of parallel top and bottom walls 27 and 28 and parallel sidewalls 29 and 30 into which the TE.sub.20 rectangular mode wave from stage A is launched. Extending from these walls are four projecting finger portions 23, 24, 25 and 26 which form an "X" cross-section stage, each finger portion being a triangular or tapered waveguide section extending from the parallel sidewalls 29 and 30 at front end 21 of stage B to output end 22 thereof. This rectangular-to-"X" tapering configuration sets up four orthogonally spaced components of the wave to be aligned with a downstream circular waveguide TE.sub.01 mode of the third or output end stage C, shown in detail in FIG. 4. As illustrated in FIG. 4, the circular waveguide TE.sub.01 mode is obtained by configuring stage C to have four tapered portions 43, 44, 45 and one not visible in FIG. 4 extending from respective input ends 33, 34, 35 and 36, which are aligned with the four sections 23, 24, 25 and not visible in FIG. 3 of the `X`-shaped output end of middle stage B. Each of sections 43-46 tapers to an output circular shape, as shown in FIG. 4, so that what is launched from output 50 of section C is a circular TE.sub.01 mode wave.
A practical problem in manufacturing a conventional Marie launcher is the high cost of making precision mandrels for electroforming the respective stages of the launcher. As described in my above referenced patent, by configuring the front stage A to have a dual integrated wedge-shape, it is possible to eliminate the use of a costly impedance matching element and simplify the manufacturing process. Unfortunately, the high manufacturing cost is not limited to the formation of the first stage A. The second or middle stage B has a highly complex surface and changing cross-sectional shape that has required the use of a precisely machined mandrel which must be destroyed in the course of its removal from the electroplated stage. Consequently, the cost of manufacture is undesirably exorbitant as a separate mandrel is required for each stage.